1. Technical Field
The present invention relates to a liquid ejecting apparatus and a head unit.
2. Related Art
As a liquid ejecting apparatus, typically, as a printing apparatus which prints an image or a document by causing ink to be ejected from nozzles, an apparatus in which a piezoelectric element is used has been known. The piezoelectric elements are provided corresponding to a plurality of nozzles in a head unit, respectively, cause ink (liquid) of a predetermined amount to be ejected from nozzles at a predetermined timing by being driven, respectively, according to a driving signal, thereby forming dots. Since the piezoelectric element is a capacitive load such as a capacitor in an electrical view, it is necessary to supply sufficient currents in order to operate the piezoelectric element in each nozzle.
For this reason, a liquid ejecting apparatus in the related art has a configuration in which a piezoelectric element is driven, by supplying a driving signal which is obtained by amplifying a source signal in an amplifying circuit to the head unit. For the amplifying circuit, there is a method in which a source signal before being amplified is subjected to current amplification using class AB amplification, or the like (linear amplification, refer to JP-A-2009-10287). However, since power consumption is large, and energy efficiency is not good in linear amplification, class D amplification has been also proposed in recent years (refer to JP-A-2010-114711).
Meanwhile, high speed printing or high resolution printing is highly desired in a printing apparatus, and in order to execute high speed printing, the number of dots which can be formed per unit hour may be increased. In addition, in order to execute high resolution printing, an amount of ink which is ejected from nozzles may be set to be small, and the number of dots which can be formed per unit area may be increased. That is, the number of dots which can be formed per unit hour and per unit area may be increased in order to execute high speed printing and high resolution printing, and for this reason, a method in which an ink ejecting frequency is increased is adopted.
In order to increase the ink ejecting frequency, it is necessary to increase a frequency of a driving signal which is supplied to a piezoelectric element. In order to cause ink to be stably ejected, by increasing a frequency of a driving signal, it is necessary to increase a switching frequency in class D amplification.
However, when increasing the switching frequency, a loss due to switching becomes large, and after all, energy efficiency in the class D amplification becomes lower than that in linear amplification, and it is not possible to obtain high energy efficiency which is an advantage of the class D amplification. Moreover, in a case in which switching in the class D amplification is set to a high frequency, there also is a problem of an erroneous operation due to noise.
When a switching frequency in the class D amplification is increased in order to increase a frequency of a driving signal which drives a piezoelectric element in this manner, it will cause many problems.